JESD204 Eye Scan

About

Validating JESD204B serial links becomes increasingly difficult at higher data rates. The quality of the line cannot be determined by measuring the far-end eye opening at the receiver pins with readily available lab equipment. Traditional oscilloscopes suitable for JESD204B testing require 16-32 GHz bandwidth and cost over $150,000.

Xilinx 7-Series FPGA GTP transceivers include integrated signal integrity blocks with PLL, TX pre-emphasis, RX AGC, RX linear equalization, RX clock data recovery, and adaptation. The 2-D Eye Scan feature provides an “on-chip scope” to visualize post-equalization signal quality.

A separate sampler adjusts horizontally (time) and vertically (amplitude) in parallel with the normal CDR sampler, enabling error counting and BER calculation across offset settings.

The utility interfaces with the JESD204 Interface Framework through the following driver components:

Source code is available at GitHub.

BERT testing

The following table shows testing duration vs. BERT rates for a 5.0 Gbps link:

BERT Rate

Bits

Duration

10-8

108

20 ms

10-10

1010

2 seconds

10-12

1012

3.33 minutes

10-17

1017

~8 months

With 8,192 pixels (64 x 128 offsets), capturing 10-8 BERT requires 2.7 minutes; 10-17 would take 5,400+ years.

Mask

The JESD204B specification defines receive keep-out masks based on channel baud rate. The vertical axis in the 2-D statistical eye diagram is in “codes”, not millivolts, since measurements occur post-equalization within the FPGA.

Installation

Debian/Ubuntu

apt-get update
apt-get install -y git build-essential gnuplot libgtk-3-dev libncurses-dev

CentOS/RedHat

yum update
yum -y groupinstall 'Development Tools'
yum -y install git ncurses-devel gtk3-devel gnuplot

Usage

Usage: jesd_eye_scan [-p PATH]
    -p     Allows setting a different directory root. Default is /.
           This is useful when running the tool remote

Local execution

~$

jesd_eye_scan &

Remote execution (X11 forwarding)

~$

ssh -X root@<board-ip> jesd_eye_scan

Remote execution (SSHFS)

mkdir /home/user/mnt
sudo sshfs -o direct_io,sync_read,allow_other \
    -o StrictHostKeyChecking=no root@<board-ip>:/ /home/user/mnt
LC_ALL=c jesd_eye_scan -p /home/user/mnt

Note

The LC_ALL=c prefix is important when running remotely, because the locale on the client system can influence the format of the data.

Output

The tool displays three main windows:

  1. Main Window — Overall eye diagram visualization

  2. Status Information — System and link metrics

  3. Lane Information — Per-lane statistics

The eye opening numbers show error-free regions in Unit Intervals (time domain) and codes (voltage scale). Heat map colors represent error density at each point.

Requirements

  • JESD204B converter

  • ZC706 or ZCU102 (local execution), or KC705, KCU105 (remote execution)

  • ADI Linux image on SD Card or ADI kernel with Microblaze RFS

Tweaking

Converter-side adjustments available:

  • JESD204B pre-emphasis

  • JESD204B CML differential output drive level

These modifications trade off eye opening, power consumption, and potential EMI emissions.

References